Use callback_forward.h instead of callback.h where possible.

base/threading/worker_pool.h

 // Copyright (c) 2011 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef BASE_THREADING_WORKER_POOL_H_
 #define BASE_THREADING_WORKER_POOL_H_
 #pragma once
 
 #include "base/base_export.h"
-#include "base/callback.h"
+#include "base/callback_forward.h"
 
 class Task;
 
 namespace tracked_objects {
 class Location;
 }  // namespace tracked_objects
 
 namespace base {
 
 // This is a facility that runs tasks that don't require a specific thread or
@@ skipping 23 matching lines @@
   // like you can for PostTask above.
   static bool PostTaskAndReply(const tracked_objects::Location& from_here,
                                const Closure& task,
                                const Closure& reply,
                                bool task_is_slow);
 };
 
 }  // namespace base
 
 #endif  // BASE_THREADING_WORKER_POOL_H_